Determination of creatinine in urine by tandem mass spectrometry

Electrospray tandem mass spectrometry (TMS) is a very powerful tool that enables one to perform high sample throughput analysis. This paper describes a method to determine creatinine in urine by tandem mass spectrometry with direct sample infusion into an ion source.

Samples (50 microl) were diluted with internal standard (IS) (450 microl of 0.667 mmol/l deuterated creatinine). Diluted samples were introduced into mass spectrometer with no prior pretreatment and after purification on ion-exchange 96-column cartridge. Tandem mass spectrometry analyses were performed in selected reaction monitoring mode. Creatinine and creatinine-d(3) were monitored using precursor and product ion settings (m/z 114 to 86 and m/z 117 to 89, respectively). The time of an analysis was 3.015 min. Both TMS methods were compared mutually and with the results obtained by enzymatic and Jaffe method.

Linearity was obtained in the range 0.06-60 mmol/l. Detection limit was 0.2 mumol/l and recoveries were in the range 95.1-98.3% for both the assays with and without ion-exchange column. Results of both assays are in good agreement with those obtained by enzymatic and Jaffe method based on log-transformed Bland-Altman plots. Electrospray tandem mass spectrometry method utilizing both approaches with and without ion-exchange column is acceptable according to CLIA criteria.

Tandem mass spectrometry allows rapid, sensitive and selective determination of creatinine in untreated urine.